In recent years, different types of radio networks have been developed to provide radio communication for various wireless terminals across different areas. The radio networks, e.g. operating according to Long Term Evolution, LTE, are constantly improved by new functionality to provide better capacity, performance and coverage to meet the demands from subscribers using services and increasingly advanced terminals, such as smartphones, tablets and laptop computers. These terminals contain a typically small and light-weight battery that provides electrical power for radio communication and application handling such as processing of input commands and play-out of media. Due to the weight and size requirements, such batteries have a very limited capacity. In particular, considerable amounts of power are consumed when transmitting and receiving radio signals to and from a serving network node. This power consumption naturally drains the battery and it is often a challenge to minimize or reduce the time that a terminal must be active and consume power to prolong battery life without losing functionality and quality as experienced by the user.
In the field of radio communication, the term User Equipment, UE, is commonly used and will be used in this disclosure to represent any terminal or device capable of radio communication including receiving downlink signals transmitted from a serving network node and sending uplink signals to the network node. Throughout this disclosure, UE could e.g. be exchanged for wireless device which is another common term in this field. The term UE should be interpreted broadly in this disclosure as a communication entity that basically communicates by radio access with network nodes. Thus, a UE in this context is not necessarily held and operated by a human user but it could also be a machine-to machine type of device operating automatically.
Further, the term “network node”, also commonly referred to as a base station, radio node, e-nodeB, eNB, etc., represents any node for providing radio access in a radio network that can communicate uplink and downlink radio signals with UEs. The radio network may, without limitation, also be referred to as a cellular network or a mobile network. The network nodes described in this disclosure may include so-called macro nodes and low power nodes such as micro, pico, femto, Wifi and relay nodes, to mention some customary examples. Throughout this disclosure, network node could e.g. be exchanged for base station.
As indicated above, various solutions are available to minimize or reduce the power consumption in a UE. A key example of that is the functionality for Discontinuous Reception, DRX, where the UE turns off and on its receiver according to a predefined DRX scheme. In this scheme, “on-duration” denotes a relatively short period when the UE's receiver must be switched on, e.g. in order to receive some message or data from the network node if needed, or to measure signals, while “off-duration” denotes a relatively longer period when the receiver can remain switched off. A DRX cycle is defined as one on-duration period and one off-duration period which both have predefined lengths. Radio signals can thus only be received by the UE during the on-duration periods but not during the off-duration periods. A main purpose of applying DRX is that the UE naturally saves power during the off-duration periods by not having its receiver switched-on, and also resources in the network will not be occupied for the UE during the off-duration periods.
The DRX feature and resulting UE behavior are governed by various DRX parameters, e.g. specifying the length of the on-duration and off-duration periods, among other things, and the DRX parameters are typically configured in the UE by signaling from its serving network node, e.g. for Radio Resource Control, RRC, which is illustrated in FIG. 1. The network node 100 thus sends valid DRX parameters to the UE which in turn goes to sleep and wakes up, i.e. in terms of reception, according to the occurrence of respective off-duration and on-duration periods as defined by the signaled DRX parameters. The UE thus performs this when it leaves an active state and enters a DRX mode which happens under certain circumstances, as defined by the DRX parameters.
In more detail, the DRX parameters typically include a parameter called “inactivity timer” which should be started after each completed activity in the UE such as transmission or reception of data or a message or a measurement. For example according to current procedures, the Inactivity timer may be started at the reception of a downlink packet and at the reception of an uplink grant. If there comes another packet just after the first one, the inactivity timer is restarted. FIG. 2 illustrates by a time-activity diagram where 200 denotes a latest activity, such as a transmission or reception, by the UE. If the UE remains inactive after this activity 200 until the inactivity timer expires, i.e. not transmitting or receiving any signals, the UE will enter a state of following the DRX cycle which is fixed in time for the UE. In this case, the UE goes to sleep when the inactivity timer expires, shown by a down arrow, and then following the fixed DRX cycle of sleeping and waking up, i.e. turning off and on its receiver, as shown by a succession of down and up arrows.
In this figure, so-called short and long DRX cycles are shown for illustrative purposes which the UE may apply according configuration. The UE is typically configured to apply the short DRX cycle initially and then the long DRX cycle later when remaining inactive even longer since the likelihood of activity decreases over time.
The radio communication of today is becoming more and more based on the Internet Protocol, IP, which means that a UE may be active in radio communication intermittently and is thus frequently switching between periods of activity and periods of inactivity. As a result, the UE may often be in the DRX sleeping state for very short periods, i.e. after the inactivity timer has expired, before it must return to active state again by turning on the receiver for receiving signals. In that case, the inactivity timer causes the UE's receiver to be on and consume power for a significant part of each inactive period. It is therefore a problem that UEs often consume considerable power even when DRX is applied. On the other hand, the inactivity timer is needed to avoid latency in the radio communication by controlling the UE to enter the DRX sleeping state not too soon when there might be further signals to receive.